Organic Chemistry/Foundational concepts of organic chemistry/Atomic structure/Octet rule and exceptions
The octet rule refers to the tendency of atoms to prefer to have eight electrons in their valence shell.
The main exception to the rule is hydrogen, which is at lowest energy when it has two electrons in its valence shell.
Other notable exceptions are aluminum and boron, which can function well with six valence electrons; and some atoms beyond group three on the periodic table that can have over 8 electrons, including sulfur. Additionally, some noble gasses can form compounds when expanding their valence shell.
The other tendency of atoms with regard to their electrons is to maintain a neutral charge. Only the noble gasses have zero charge with filled valence octets. All of the other elements have a charge when they have eight electrons all to themselves. The result of these two guiding principles is the explanation for much of the reactivity and bonding that is observed within atoms; atoms seeking to share electrons in a way that minimizes charge while fulfilling an octet in the valence shell.